The present invention relates generally to medical and surgical devices, systems and methods. More specifically, the invention relates to devices, systems and methods for enhancing knee surgery procedures, in particular, knee replacement procedures and specifically revision total knee replacement procedures.
The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues, including ligaments, within and surrounding the knee joint. The knee is generally divided into three compartments: medial (the inside part of the knee), lateral (the outside part of the knee), and patellofemoral (the joint between the kneecap and the femur). The medial compartment comprises the medial joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The lateral compartment comprises the lateral joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The patellofemoral compartment comprises the joint between the undersurface of the kneecap or patella and the femur. Four ligaments are especially important in the stability, alignment and functioning of the knee: 1) the anterior cruciate ligament; 2) the posterior cruciate ligament; 3) the medial collateral ligament; and 4) the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia is often worn away, allowing the femur to directly contact the tibia. This bone-on-bone contact can cause significant pain, discomfort, and disability for a patient and will often necessitate knee replacement or knee arthroplasty.
Under certain circumstances, a previously implanted prosthetic knee joint may need to be replaced by a new prosthetic knee joint in a procedure called knee revision surgery or revision TKA. Common causes for needing revision TKA include: infection, instability, including specifically flexion instability, femoral component mal-rotation causing poor patellar tracking, and loosening of the prosthetic implants from the bone to which they were attached. Instability is often attributable to poor balancing of the soft tissue during the index or primary TKA.
Revision TKA procedures share some similarities with TKA procedures with respect to components being implanted, such as the prosthetic femur, tibia, and patella. In revision TKA, the old femoral component and tibial component of the prosthetic knee joint are most often removed. Removing the old prosthetic components can be very time consuming, and often large segments of bone may come off with the removed prostheses. As such, empirical landmarks that might otherwise be used to reference proper balance and position for the revision TKA femoral and tibial components are often undistinguishable. The quality of the femoral bone uncovered during revision TKA is often severely osteoporotic, lacking external structural integrity often due to stress shielding caused by poor balancing. Bone quality is enhanced by normal compressive stress forces, conversely, bone quality will deplete if the bone is shielded from those same stress forces.
Like with TKA, a challenge in revision TKA is to properly balance ligament tension, especially in the medial and lateral collateral ligaments, through a full range of motion of the knee, for example, from a fully extended to a fully flexed position, or vice versa. The collateral ligaments, which connect the distal femur and the proximal tibia on the medial and lateral aspects of the knee, account for much of the stability and movement of the knee. If one of the collateral ligaments is too lax or too tight relative to the other collateral ligament, the knee will typically be unstable, range of motion may be limited, the patella may track improperly, and/or the femur and tibia may wear unevenly, leading to arthritis and pain which may often necessitate another repeat surgery. Thus, it is imperative for the short and long-term success of a revision TKA procedure to achieve balanced ligament tension in the knee through a full range of motion.
Balancing ligament tension during any knee replacement surgery is complicated by the fact that the natural knee does not operate like a hinge moving about a single axis. The knee exhibits dynamic external rotation of the tibia relative to the femur as the knee moves from its flexed to its fully extended position. This automatic rotation of the tibia occurs in the opposite direction when the knee is flexed from its fully extended position to produce an internal rotation of the tibia relative to the femur. Thus, the natural knee exhibits a rotary laxity that allows the tibia to rotate through a limited internal and external arc, during knee flexion. Additionally, the femur translates anteriorly and posteriorly as the tibia is being flexed about the femur, bringing yet another movement variable. Thus, the ligaments of the knee, along with the femur, tibia and patella create a dynamic bio-mechanism, making ligament tension balancing in knee replacement surgeries challenging. Many articles and studies have been devoted to ligament tension balancing in TKA, such as: Mihalko, W. H. et al., Comparison of Ligament-Balancing Techniques During Total Knee Arthroplasty, Jnl. Bone & Jt. Surg., Vol. 85-A, Supplement 4, 2003, 132-135; Eckhoff, D. G. et al., Three-Dimensional Morphology and Kinematics of the Distal Part of the Femur Viewed in Virtual Reality, Jnl. Bone & Jt. Surg., Vol. 85-A, Supplement 4, 2003, 97-104; and Ries, M. D. et al., Soft-Tissue Balance in Revision Total Knee Arthroplasty, Jnl. Bone & Jt. Surg., Vol. 85-A, Supplement 4, 2003, 38-42.
Balancing a knee specifically during revision TKA is further complicated by the poor quality of bone often encountered and/or missing portions of the bone itself. Balancing techniques and instruments for balancing a knee during revision TKA often reference from the femoral intramedullary canal, specifically due to the fact the external femoral bone quality is not suitable for fixating balancing instruments. Additionally, the femoral intramedullary canal is often used to establish the anterior-posterior location of the replacement femoral component.
The components of a revision TKA femoral knee prosthesis may be selected to have specific sizes and to be specifically positioned to balance ligament tension. Revision TKA procedures may involve making further distal cuts across the distal end of the femur, anterior and posterior cuts, and angled anterior and posterior chamfer cuts to help secure the femoral component solidly in place. The surgeon attempts to make these femoral bone cuts to achieve a position and orientation of the femoral prosthetic component so as to optimally balance ligament tension through a full range of motion of the knee, and to achieve balance specifically of and between the flexion axis and the extension axis. However, it is often very challenging to position the femoral bone cuts and femoral prosthetic component to provide ideal ligament tension through the full range of motion of the knee. This is due primarily to a “trade-off” often facing the surgeon between optimal fixation vs. optimal soft-tissue balancing. Secure fixation is required, but if chosen at the expense of proper balancing, there is a distinct possibility the revision TKA will also fail for some of the same reasons as the primary knee including poor balancing leading to flexion instability and/or stress shielding, for example. The human femur has a natural bow or radius of approximately 70-120 cm along its length. Due to the natural radius of the femur, placing a long intermedullary rod up the femoral intramedullary canal to establish the anterior-posterior (A-P) location of the femoral component often results in the rod skiving anteriorly as it is inserted deep into the femoral diaphysis while also shifting posteriorly outside the distal femur. Locating off of this rod, or establishing the A-P location of the femoral component off of the rod in such a skewed position, will compromise the balance of the knee between the flexion axis and the extension axis.
A number of devices and techniques have been described that attempt to facilitate ligament balancing during a TKA procedure. These devices and techniques may also find use for revision TKA procedures. Some techniques, such as those described in U.S. Pat. No. 5,733,292, involve trial prosthesis components which are used after femoral and tibial bone cuts are made to assess ligament tension. Some devices, such as those described in U.S. Pat. No. 6,758,850, are used to measure a gap between the distal femur and proximal tibia in extension and to help a surgeon recreate that same gap when the knee is in flexion. Other “gap checking” devices are described in U.S. Pat. No. 6,575,980. Other devices have been developed to help measure an amount of ligament tension or to apply a desired amount of tension to the ligaments. U.S. Pat. No. 4,501,266, for example, describes a knee distraction device for applying a desired amount of tension. Many paddle-like devices have been suggested for applying or measuring tension across a knee joint, such as the devices described in U.S. Pat. Nos. 5,597,379; 5,540,696; 5,800,438; 5,860,980; 5,911,723; and 6,022,377. Other methods and devices include those described in co-assigned U.S. Pat. Nos. 7,442,196, and 7,574,821, as well as co-assigned and co-pending U.S. application Ser. No. 11/149,944 , Ser. No. 12/544,897 , and Ser. No. 12/609,666 each of which are incorporated herein by reference.
Additional information relating to attempts to address the problems described above may be found in U.S. Pat. Nos. 5,470,354; 5,656,785; 7,104,996 and U.S. Patent Application Publication Nos. 2005/0209605; 2005/0240196; 2005/0267485; 2006/0241569; 2007/0219559: 2007/0232959; and PCT Publication Nos. WO 2005/089681; WO 2005/037121; WO 2006/047005, for example. However, each one of these references suffers from one or more of the above-identified disadvantages.
For at least the above reasons, a need exists for improved devices, systems and methods for enhancing knee replacement surgery and specifically for dynamically balancing ligaments during knee replacement to improve range of motion, stability, and patellar tracking of the prosthetic knee joint. Additionally, such devices would allow for secure fixation to the femur via the intramedullary canal, without being biased by the natural bow of the femoral canal, and without the intramedullary canal dictating the balance point of and between the flexion axis and the extension axis of the femur. Ideally, such devices and methods would allow a surgeon to achieve a desired ligament tension balance before committing to and making final bone cuts to the femur. Such devices would ideally be simple to use in conjunction with existing knee replacement procedures and equipment such as prosthesis templates, measurement guides, cutting guides, and saw blades or burs. At least some of these objectives will be met by the present invention.